Fairly effective clamps for joining and sealing tubular conduits such as truck exhaust pipes in end-to-end relation using stretchable metal bands are known. For example, U.S. Pat. No. Re 30,042, owned by the assignee herein, discloses a method and apparatus for joining two tubular members using a band of ductile metal passed around the ends of the tubular members and circumferentially stretched beyond its elastic limit to conform with the outer surfaces of the members throughout practically their entire circumferences. Other structures using ductile metal bands are known, for example, in the Cassell U.S. Pat. No. 3,905,623. One embodiment of the Hiemstra patent is shown in FIG. 1 as comprising a metal band 10 welded to reinforcing bars at each end at spot welds 16 and 16'. Holes for threading a nut and bolt through the metal band and reinforcing bars when the apparatus is wrapped around the tubular members where pipes to be joined are shown at 18 and 18'.
Typically, the existing metal band-type clamps will use a fairly high-quality metal such as a stainless steel, e.g. 304 SS ductile strap. Aluminized steel is also used, but currently is used primarily as part of a prestretched, curved clamp. Using 304 stainless steel has the advantages of resisting corrosion, being securely weldable to reinforcing bars, and having sufficient ductility to withstand elongation before tearing or breaking. A less ductile metal band may tear or break under the stress applied to the metal band when the band is wrapped around the tubular members and circumferentially stretched to form a coupling and sealing joint. The reinforcing bars are typically made of plated metal to withstand corrosion on the exposed surfaces of the bar in use. Moreover, the reinforcing bar must also be capable of being securely welded to the metal band.
Metals having a lower tolerance than stainless steel for elongation or stretching before ripping or breaking are commonly available. Metals other than stainless steel are available which are non-corroding. Some of these metals are not capable of being welded as readily as stainless steel. Moreover, reinforcing bars are available which are not plated but are more susceptible to corrosion. However, use of these materials has the advantage of reducing material costs in many instances.
In manufacturing and using the metal band-type pipe joints, it is desirable to reduce the stress on the clamp to allow use of lower cost materials. Reductions in stress are particularly important in the region where the clamp is joined together, since this is one of the higher stress regions of the clamp. It is also desirable to strengthen the clamp in its high-stress areas, again including the region where the clamp is joined together. Moreover, it would be advantageous to save or reduce the labor required in manufacturing the metal band-type clamps, such as by eliminating or reducing the amount of welding necessary. It is also desirable to reduce or eliminate opportunities for corrosion of the clamp or to enable the use of materials which are of a lower cost due to a lack of plating or other corrosion preventatives. It is further desirable to accomplish these objectives in an aesthetically pleasing structure which can be made in an economical way.